1. Field of the Invention
The present invention relates to a controller for a homogeneous charge compression ignition internal combustion engine which compresses a fuel-air mixture of a fuel and air to make a spontaneous ignition.
2. Description of the Related Art
In recent years, a homogeneous charge compression ignition internal combustion engine, which is generally called as an HCCI engine, has drawn attention as an engine with high efficiency and less discharge such as nitroxide or the like. The homogeneous charge compression ignition internal combustion engine (hereinafter, referred to as the HCCI engine where appropriate) compresses a fuel-air mixture of a fuel and air to a high temperature in a combustion chamber of a cylinder to make the fuel-air mixture spontaneously ignited to combustion.
In this type of HCCI engine, proceeding of a chemical reaction (oxidation reaction) on the fuel-air mixture tends to vary according to various contributing factors such as a temperature condition in the cylinder, an air-fuel ratio of the fuel-air mixture, an octane number of a fuel and the like. Particularly, in a working state where a desired torque (load) of the HCCI engine is relatively great, a combustion timing range possible for an appropriate working of the HCCI engine without knocking or extinction is narrow. Thereby, it has become a great challenge how to control a combustion timing of the fuel-air mixture at an appropriate timing.
Thus, as a control technology of this type of HCCI engine, there has been known one disclosed in, for example, Japanese Patent Laid-open No. 2004-346796 (hereinafter, referred to as Patent Document 1), Japanese Patent Laid-open No. 2004-353485 (hereinafter, referred to as Patent Document 2) or in Japanese Patent Laid-open No. 2000-179368 (hereinafter, referred to as Patent Document 3). The control technology disclosed in Patent Document 1 or 2 adjusts oxygen concentration and temperature in the cylinder by controlling an amount of exhaust gas recirculated in an intake air system (EGR gas). As a result, the fuel-air mixture may be controlled to combust at an appropriate timing. Further, the control technology disclosed in Patent Document 2 is configured to control each of two intake valves disposed in each cylinder of the HCCI engine independently; therefore adjusts the amount of EGR gas recirculated in the intake air system by controlling separately lifting amount and valve-open timing of the intake valves in a transient working state where the load of the HCCI engine varies. As a result, the combustion timing of the fuel-air mixture may be controlled at an appropriate timing even though the HCCI engine is in the transient working state.
According to the control technology disclosed in Patent Document 3, two types of fuels having mutually different octane numbers may be supplied independently and separately to a cylinder of an engine, and a supplied proportion of the respective fuel is adjusted according to a load of the engine. Thereby, the ignition and combustion of the fuel-air mixture are stabilized in a wide working area varying from a low-load area to a high-load area.
As aforementioned, the proceeding of a chemical reaction on the fuel-air mixture varies according to the above-mentioned various factors in the HCCI engine. Therefore, for a HCCI engine having a plurality of cylinder particularly, it is easy to have a variation on the combustion timing between each cylinder (irregular variations with respect to a desired combustion timing for each cylinder), and consequently causing a variation on output torque of each cylinder.
However, since the control technology disclosed in Patent Document 1 recirculates the EGR gas separately in the intake air system in each cylinder, it is extremely difficult for the control technology disclosed in Patent Document 1 to inhibit the variation on the combustion timing between each cylinder due to a variation on a feature of the intake air system in each cylinder, a variation on a distribution of the EGR gas recirculated in the intake air system in each cylinder, a variation on an operation feature of a supply valve for the EGR gas in each cylinder, a variation on a response lag for the supply of the EGR gas with respect to the operation of the supply valve and so forth.
Further, a mechanism for controlling separately the intake valves of each cylinder is needed for the control technology disclosed in Patent Document 2, there brings a problem that the mechanical configuration of the HCCI engine may become complicated, leading to an expensive cost for manufacturing the engine.
Furthermore, the control technology disclosed in Patent Document 3 adjusts only the proportion between the supplied quantity of the high-octane fuel and the supplied quantity of the low-octane fuel simply according to the load of the HCCI engine. Thereby, it is difficult to inhibit the variation on the combustion timing between each cylinder even though the control technology disclosed in Patent Document 3 is applied to the HCCI engine having a plurality of cylinders.